Gas turbine engines, such as those used to power modern commercial aircraft or in industrial applications, include a compressor for pressurizing a supply of air, a combustor for burning a hydrocarbon fuel in the presence of the pressurized air, and a turbine for extracting energy from the resultant combustion gases. Generally, the compressor, combustor and turbine are disposed about a central engine axis with the compressor disposed axially upstream of the combustor and the turbine disposed axially downstream of the combustor. For a turbofan gas turbine engine, a large diameter fan is mounted to the engine shaft forward of the compressor. Air drawn into the engine passes axially through the fan and the compressor into the combustor wherein fuel is combusted in the air to generate and accelerate combustion gases which pass through the turbine and out the exhaust nozzle of the gas turbine engine. In the turbofan version of the gas turbine engine, a portion of the air flow into the engine is delivered to the compressor to pass through the engine core, while the remainder of the air passes through a bypass duct thereby bypassing the compressor and engine core.
The compressor and the turbine modules include a plurality of stages, each stage including a plurality of blades mounted to a rotor disk mounted to a rotatable shaft. One or more stages of blades may be associated with a single rotor disc. In many gas turbine engines, the compressor and/or turbine rotors constitute integrally blade rotors (IBR) wherein the blades are machined from an oversized rotor disk forging, metallurgically joined or solid state welded to a rotor disk, rather than being mechanically secured to the rotor disk, such as by a dove-tail or fir-tree blade root fit into a correspondingly shaped slot in the rotor disk. Consequently, an integrally bladed rotor assembly is lighter than a conventional bladed root rotor assembly of comparable size.
However, rotor blades are subject in service to damage from impact by foreign objects ingested into the engine, commonly referred to as foreign object damage (FOD). Rotor blades are also subject in service to damage from impact by pieces of broken or unsecured engine parts entrained in the air flow passing through the engine, commonly referred to as domestic object damage (DOD). Because of the position at the forward end of the gas turbine engine, fan and compressor damages are particularly susceptible to foreign object damage, as well as domestic object damage from pieces of blades broken off upstream blades. While minor damage may be repaired relatively easily by a process known in the art as blending, blades that suffer significant damage from an FOD/DOD event must be replaced.
Replacement of blades on integrally bladed rotors has proven to be troublesome. In a common repair method, after an integrally bladed rotor having a damaged blade requiring replacement is removed from the engine, the damaged portion of the damaged blade is removed leaving a blade stub projecting outwardly from the rotor disk. The blade is then restored by metallurgically bonding a replacement blade section to the blade stub. Although a number of variations of the aforedescribed method for repairing a damaged blade on an integrally bladed rotor have been proposed and tried in military and commercial applications, consistently obtaining a structurally sound repair with original equipment manufacture properties has proven to be elusive. For example, U.S. Pat. Nos. 4,873,751; 5,109,606; 5,197,190; 5,755,031 and 6,536,110 disclose various techniques for repairing damaged blades of integrally bladed rotors by welding a replacement blade section to a blade stub on the rotor. U.S. Pat. No. 6,354,482 discloses a linear friction welding apparatus suitable for use in bonding an airfoil to a rotor during manufacture of an integrally bladed rotor and U.S. Pat. No. 6,244,495 discloses a gripper for use in connection with a linear friction welding apparatus.